Asthma is characterized by an inappropriate immune response manifested as enhanced accumulation of immune cells in the airway. In general, the immune response has been divided into innate and adaptive components, and recent evidence indicates the innate immune response generates inflammatory mediators that provide critical immunomodulatory signals to the adaptive immune system. In the particular context of the inflammatory response to inhaled materials, we have proposed the airway epithelial cells represent an ideal candidate to act as a primary sentinel site in innate immunity. This possibility was derived from observations that these cells express a network of immune-response genes that provide critical immunomodulatory and biochemical signals for immune cell influx, activation, and retention in the airway. The current proposal is based on several novel findings related to a member of the interleukin (IL)-12 family, called IL-12 p80 (p80). We identified the airway epithelial cell as a novel cellular source for p80 production following cytokine administration, infection with Sendai virus, and in subjects with asthma. Furthermore, Sendai viral infection of mice that lacked another IL-12 family member (IL-12 p35) overproduced p80 and displayed inappropriate inflammation characterized by enhanced accumulation of macrophages in the airway. Interestingly, in asthma subjects, but not normal or chronic bronchitis patients, we again found p80 overproduction that correlated with enhanced macrophage accumulation. Further studies demonstrated p80 functions as a macrophage chemoattractant and the IL-12 receptor beta 1 chain (IL-12Rbeta1) is necessary and sufficient to generate this p80-dependent chemotactic response. Taken together, our results associate p80 overproduction with excessive viral and asthmatic inflammation, new functional consequences of p80 production in vivo, and p80-dependent immunomodulatory properties, such as macrophage chemotaxis, that are mediated through IL-12Rbeta1 signaling. Accordingly, the aims of this proposal are to define p80-dependent macrophage accumulation following SdV infection and characterize the proteins that mediate this response. In addition, we will define the structural components of IL- 12Rbeta1 that mediate p80-dependent chemotaxis. These studies will provide insight into the pathogenesis of inappropriate viral and asthmatic airway inflammation, and exploitation of this knowledge will provide the framework to develop selective regulators of p80 function in order to modulate this inflammation.